During the Start of Day charge, the University of Michigan sees on-and-off clouds to the East. Eventually, they clear up. Aurum didn’t get the best charge, but it got something, and Strategy’s weather models predict sun the entire day.
Aurum drives at about 45 miles per hour for around three hours before pulling in at 11:30 AM to the End of Stage Two location at Republic High School in Republic, Missouri.
The weather models had predicted accurately; the sun beats down on the Solar Car Team and the temperature hovers at around 95 degrees Fahrenheit.
But the team can’t take advantage of it.
When Michigan tries to charge Aurum during its allotted 15 minutes, something goes wrong. The first minute goes smoothly: Michigan manages to empty the car of its driver, point the array towards the sun, and change the battery pack configuration, readying Aurum for charge. But once Aurum begins charging, the race electrical engineers notice that despite the sunny conditions, only about 20 Watts of power come through the array, a far cry from the typical 1000 Watts that they had expected. Effectively, the car cannot charge.
The first thing that comes to mind: is there a problem with the Maximum Power Point Trackers? Maximum Power Point Trackers (MPPTs) are responsible for maximizing the array’s production of charging power by maximizing the power output of the solar cells. Using a transformer, MPPTs also match the output voltage from the array to the required input voltage of the battery.
The Electrical team decides to turn off the solar array in order to identify the charging problem’s source. When the array shuts off, something unexpected follows suit: the entire car. “This instantly confused everyone and made our problems seem much worse,” Race Electrical Engineer Lucas Rudd explains. “This is not the normal case. The car can support its own power through the battery alone.”
The electrical engineers put their heads together and conclude that since the car was not supporting itself on battery power, the battery was most likely the issue, not the MPPTs.
Michigan lets officials know about its battery problems and asks if it can work to fix the battery now. But the University of Michigan cannot. In accordance to race regulations, after its 15 minutes are up, Michigan must impound the faulty battery by locking it into a box; this rule prevents any team from cheating by charging their battery more than the competition. Only when the End of Day charge begins at 6:00 PM can the University of Michigan again work on the battery.
Michigan forfeits its 15 minute charge and instead focuses its full attention on trying to diagnose in this small amount of time, scrambling to test as much as possible in order to gain a better understanding of the problem. All of the team’s electrical engineers gather around the car with laptops, trying to piece together an idea of what is going on, and moving fast, trying to gather data while they still have the battery to work with.
The 15 minutes run out. Now, a new clock starts: the team has five hours to figure out what to do—without touching the battery.
The Electrical team joins Head Strategist Alan Li in the Chase vehicle to assess telemetry data in an attempt to pinpoint the origin of the problem. They bounce ideas off of one another and come up with two viable explanations: 1) there is a problem with one of the relays, which open and close circuits, or 2) there is a problem with a fuse. Michigan’s relays are reliable, durable; Electrical concludes that they are not the problem, and that one of the fuses in the battery blew. The race battery has three fuses, one low-voltage, two high. Unfortunately, Electrical is unable to use the telemetry data to divine what caused the faulty fuse to break or even to discern which fuse was the broken one.
Looking at the time intervals between the actions taken immediately prior to the problem’s inception, the electrical engineers manage to narrow it down to the two high-voltage fuses. But they don’t know which fuse out of these two is broken.
Luckily, Michigan comes prepared; the team brought a second, nearly identical battery pack for testing purposes. Electrical fiddles with different parts of this spare battery to try and recreate the conditions that arose on the race battery pack. One at a time, Electrical removes the fuses, testing to see if one or the other results in a replication of the race pack’s behavior. Removing the positive high-voltage fuse results in the behavior most similar to that of the race pack.
Now that the Electrical team has identified the likely root of the charging problem, it methodically choreographs a procedure to replace the fuse as swiftly and seamlessly as possible, dividing up and delegating specific tasks to specific people and rehearsing the repair procedure on the spare battery. Lucas has worked most closely with the race battery in the past, so the team decides he will be the one to actually perform the repair, while others assist him with diagnosis, tool accessibility, and more.
Stakes are high. “It’s the kind of thing where if you do it wrong, it’s the end of the race,” Business Director Sarah Zoellick notes. “On top of that, you’re dealing with what is basically a small bomb.” It’s true; if the team messes up badly, the battery will likely catch fire, and could explode. It has the explosive power of roughly twenty hand grenades.
While Electrical prepares and plans for 6:00 PM, the Strategy team reckons with the implications of different possible outcomes. The question is whether the Electrical team can get the battery fixed before the End of Day charge time runs out, and how its performance will impact the race going forward. Alan runs simulations assessing three situations. Situation One: Electrical manages to fix the battery very quickly and Aurum gets to charge for almost the full two hours of End of Day charge—End of Day charge is fine and the following Start of Day charge is fine. Situation Two: Electrical doesn’t manage to fix the battery quickly enough for Aurum to take advantage of End of Day charge, but fixes it in time for Start of Day charge the following morning—End of Day charge is compromised, but Start of Day charge is fine. Situation Three: Electrical doesn’t manage to fix the battery until the end of Start of Day charge—End of Day charge is compromised, Start of Day charge is compromised.
In the half-hour leading up to the End of Day charge, the remainder of the team readies itself for pointing the array in the event of the best case scenario—Alan’s Situation One. The electrical engineers and driver/Engineering Director Clayton Dailey gather replacement fuses and relays. They lay out toolboxes filled with Vector tools—multi-meters and wrenches and electrical tape and anything else that could come in handy. They call over an official to oversee the repair. They pull up the necessary specifications and schematics, don safety glasses and surgical gloves, and get into their individual designated positions. Michigan is ready.
The clock strikes 6:00 PM. An official’s voice: “Three. Two. One. De-impound!” It begins. The electrical engineers open the lock box and take out the race battery. Several gloved hands descend upon it—everyone knows their job. The Electrical team tests the positive high-voltage fuse for continuity and finds none; the circuit is broken, and this is the blown fuse. They were right. Lucas calls for tools and others hand tools to him— “It looked like a surgical operation from TV,” Crew Chief Perry Benson describes. Everyone assisting with the repair is calm, collected, focused. Electrical un-tapes the two ends of the blown fuse, unbolts it from the wires on either side, and removes it. Electrical then replaces it with a new fuse, reconnects everything inside of the battery, tapes everything, seals it all up, closes the battery, tries turning it on to check that the repair is successful—(it is)—and then, plugs the battery back into the car. The car powers up, ready for charge. Done. Eleven minutes and forty-five seconds.
Once Aurum is charging, the team relaxes a little. “Every electrical engineer took a moment to breathe again,” Lucas describes. “We were able to relax again now that the car was once again competitive.” Alan’s Situation One—the best case scenario—had played out, and better than anyone could have hoped; Aurum gets a solid hour and fifty minutes of charge.
This, Clayton declares, “was one of the quickest and smoothest repairs we have ever made to the car.” Generally, performing electrical repairs on the car is a long, convoluted process. “The officials were all pretty impressed with us,” Alan adds. “We were all pretty impressed with ourselves.”
Lucas expands on the gravity of the situation: “It was the single most stressful event of race crew, and quite possibly of my entire life. But it was also one of the greatest feats of problem-solving I have ever been a part of.” Lucas notes that Michigan had just reached the halfway point. “We were racing a great car with a great team supporting it, and everything we worked towards all year long was almost lost… There was a very real chance of us not finishing the race. Everyone worked really hard to make sure that wouldn’t happen.”
Once again, when faced with extraordinary circumstances, the University of Michigan Solar Car Team proves it has the diligence, the training, and the level-headedness to persevere and come stronger out the other side.